The present invention relates to a permanent magnet rotary machine and an electric vehicle using the permanent magnet rotary machine.
In a permanent magnet rotary machine, a "cogging torque" due to a magnetic fluctuation of a stator and a rotor causes and there is a problem the cogging torque obstacles a smooth rotation.
To improve a reduction in the cogging torque, a permanent magnet rotary machine is disclosed in Japanese patent application laid-open publication No. Hei 3-45,140, in which since a groove is provided on a permanent magnet a magnetic fluctuation component for generating a cogging torque having the same dimensional degree number to a generated cogging torque and having a reverse phase is provided on a permanent magnet magnetic field.
Further, without the permanent magnet rotary machine structure in which the magnetic fluctuation component is kept to the permanent magnet magnetic field, a permanent magnet rotary machine is disclosed, in Japanese patent application laid-open publication No. Hei 5-103,453 and Japanese patent application laid-open publication No. Hei 7-336,917, in which a fluctuation component such as a hole or a groove on a surface of a rotor iron core which is positioned at an outer periphery of a permanent magnet.
In a former Japanese patent (Japanese patent application laid-open publication No. Hei 5-103,453), a hole extending to an axial direction is provided at a position of the rotor iron core which corresponds to electrical angle s of 60 degree and 120 degree of the rotor iron core. Namely, a torque of a portion, which is a peak position of a torque ripple, is made small and as a whole the torque is formed uniformly, as a result a reduction in the vibration and a reduction in noises are improved.
In a latter Japanese patent (Japanese patent application laid-open publication No. Hei 7-336,917), in a rotor iron core in which a convex portion of an arc shape permanent magnet is directed to a rotation center, a slit for extending to a radial direction is formed at a portion which is positioned at a side of a convex portion of the permanent magnet. By the provision of the slit, the magnetic resistance of the slit formed on the portion is increased, the magnetic flux passing to the slit formed on the portion is reduced, and further the inductance of the stator windings is reduced, as a result a restraint of the torque lowering is attained.
Further, in an electric vehicle using a permanent magnet rotary machine, a smooth deceleration and a smooth standstill of the electric vehicle are difficult by a cause of the cogging torque generated in the permanent magnet rotary machine. Accordingly, in the electric vehicle it is necessary to provide a mechanism for cutting a connection between a rotating shaft of the permanent magnet rotary machine being a power source and a wheel or a wheel drive shaft during a deceleration time and during immediately before the standstill of the electric vehicle and a mechanism for absorbing the vibration.
In the technique shown in Japanese patent application laid-open publication No. Hei 3-45,140, the cogging torque can be reduced but since the groove is provided on the permanent magnet itself, following problems cause.
First of all, as a first problem, when the permanent magnet is processed, the cracks and the crevices are easily caused according the material and then the mechanical strength lowers. As a second problem, since the groove is formed on the surface of the permanent magnet, so as to fully reduce the cogging torque, it is necessary to form a large scale groove. As a third problem, in case of a latter magnetization, namely the permanent magnet is magnetized after a formation of the rotor, when the groove is existed on the surface of the permanent magnet, since an uniform magnetization is difficult, the performance as the permanent magnet lowers.
Further, in the technique shown in Japanese patent application laid-open publication No. Hei 5-103,453, a whole torque can be uniformed, however since the hole is provided at the portions of the electrical angle of 60 degree and 120 degree, the cogging torque cannot be effectively reduced.
Further, in the technique shown in Japanese patent application laid-open publication No. Hei 7-336,917, in the permanent magnet rotary machine, the convex portion of the arc shape permanent magnet is arranged to direct for the center of the rotor, and in this structure it aims the improvement in the particular magnetic path, however the cogging torque of the rotary machine having the above stated arrangement structure is not effectively reduced.